The connectivity was lost at the plate member interface. You can use the parametric modelling feature to mesh the plate retaining proper connectivity with surrounding entities. Click on the modified model as attached which is meshed by the parametric…

There are multiple structures in the model- this is because of the reason that the plates are not connected with the beams. Please refer to the attached modified model. 5824.a4.std

I saw the rendered view of your model. It appears that you had created the channel sections placed back to back having some gap in between. Now when your are placing this channel arrangement on the column head, program would connect the shear center of…

Dear Arthur, I have gone through your model and found 1 warning and 2 Notes. 1. Warning: The warning is the about a line width of STAAD. As you can note down that the input width that is allowed in a line in STAAD Editor file is 79. The warning appears…

Dear Arthur, Please find the attached file with no such warnings. be 27.06.16.std

Dear Arthur, Please find the attached file with no such warnings, only one modification (the same mentioned in my above post) have been made in the input file. 6254.be 27.06.16.std

The maximum input width is considered as 79 columns and spaces contribute towards that width limit too.

How you connect the extension to the existing structure, is more of a detailing issue than an analysis one. For analysis purpose, you just need to ensure that the extension uses the existing nodes as one of it’s incidence nodes. As long as that happens…

Your structure has the insatiability condition arsing out of two reasons. (1) The support is pinned and the structure is laterally unstable as as no lateral frame,bracing or struts exists. You need to laterally confine the support along the lateral…

This is not related to the instability warnings, but your wind loads seem to be very high, so you may want to double check if you applied wind loading in the correct units.

I modified the model a little bit. I tried to connect the plates with beams. The entire structure will topple if there is any force from Z direction and the supports are not capable of taking any moments. I assigned a fixed support to one of the supported…